Many kinds of transparent touch panels enabling interactive input have been put into practice as one of man-machine interfaces. Examples of the transparent touch panel include, for example, an optical-type, an ultrasonic-type, a capacitance-type and resistance film-type touch panels, according to a position-sensing system.
Such a transparent touch panel uses a transparent electroconductive laminate obtained by stacking a transparent electroconductive layer and the like on at least one surface of a transparent organic polymer substrate.
As the transparent organic polymer substrate, an organic polymer substrate having high transparency is used, and examples thereof include a cellulose-based film such as triacetyl cellulose (TAC) film, a polyester-based film such as polyethylene terephthalate (PET) film, a polycarbonate-based film, and an amorphous polyolefin-based film.
Such a transparent organic polymer substrate has a low surface hardness, and is susceptible to scratching, and therefore a resin layer, which is a hardcoat layer, is coated on a surface of the transparent organic polymer substrate. This hardcoat layer is known to be effective not only for protecting the surface of the transparent organic polymer substrate, but also for flattening the surface of the transparent organic polymer substrate by filling fine scratches thereon. With respect to the hardcoat layer, it is known to conform the refractive index of the hardcoat layer with the refractive index of the transparent organic polymer substrate, and thereby suppress coloring interference due to reflection at the interface between the hardcoat layer and the transparent organic polymer substrate (Patent Document 1).
A transparent metal oxide layer such as ITO (indium-tin oxide) is generally used as the transparent electroconductive layer. In the case of directly stacking such a transparent electroconductive layer on the transparent organic polymer substrate, coloration of light passing through the transparent electroconductive laminate occurs, for example, due to optical interference resulting from reflection at the interface between the substrate and the transparent electroconductive layer or at the interface between the transparent electroconductive layer and air, or due to light absorption by the transparent electroconductive layer itself. For example, with a transparent electroconductive layer having a film thickness of approximately from 20 to 30 nm that is generally employed, the transmitted light may be colored to a slightly brown-tinted color. Such coloration causes a change in the color hue on a display screen, and therefore is not preferred.
In order to solve this problem, by inserting an optical interference layer between a transparent electroconductive layer and a transparent organic polymer substrate suppression of reflection or the like due to the transparent electroconductive layer by using the interference effect can be obtained (see, for example, Patent Documents 2).
Among position-sensing systems for a touch panel, the resistance film-type touch panel has a simple structure and an excellent price/performance ratio, and therefore a most popular. The resistance film-type touch panel is an electronic component fabricated by holding two transparent substrates, which have transparent electroconductive layers respectively located on the oppositing surface thereof, with a constant distance therebetween. By pressing a movable electrode substrate (electrode substrate on the viewing side) with a pen or a finger to sag the movable electrode substrate, contact and electrical conduction between the movable electrode substrate and a fixed electrode substrate (electrode substrate on the opposite side) are achieved, and a sensor circuit is then allowed to detect the position, thereby effecting a predetermined input.
Also, among position-sensing systems of the touch panel, the capacitance-type touch panel allows for multipoint sensing, and therefore is believed to be a promising technique in the future. According to the capacitance-type transparent touch panel, the position is sensed based on a change in the capacitance between patterned transparent electroconductive layer and a finger or the like, and a predetermined input is thereby performed.
With respect to the resistance film-type touch panel, a so-called analog-type touch using a non-patterned transparent electrode is conventionally used in general for a single-point sensing system, but in order to enable multipoint sensing, a device using a patterned transparent electrode has been also developed.
In the case where, as in these transparent touch panels for multipoint sensing, a patterned transparent electroconductive layer is used in a transparent touch panel, the transmittance or color tone of display light differs between a portion having the transparent electrical conductive layer and a portion not having it. This phenomenon causes the pattern of the electroconductive layer to be visually recognized, and thereby the display light is disturbed (hereinafter, the problem is sometimes referred to “skeleton visibility”).
In order to suppress the skeleton visibility, it is known, for example, to use a relatively thin transparent electroconductive layer (Patent Document 7), or to provide, between a transparent electroconductive layer and the underlying hardcoat layer, a layer having a refractive index intermediate between refractive indexes of these layers (Patent Document 8).
Incidentally, a transparent organic polymer substrate for a transparent electroconductive laminate, when as-is used, lacks the lubricity for handling, and therefore a lubricating layer having an uneven surface is generally used to enhance the lubricity. However, in the case of improving the lubricity by an uneven surface, diffused light reflection occurs on the surface, and this decreases the transparency and increases haze. Accordingly, it is very important to provide an organic polymer substrate having excellent lubricity, while maintaining high transparency and small haze.
As a general technique for forming a lubricating layer on a transparent organic polymer substrate, it is known to incorporate, in a resin, fine particles having a submicron particle diameter, for example, inorganic particles such as silica particles, calcium carbonate particles and kaolin particles, and/or an organic particles such as silicone particles and crosslinked polystylene particles, and thereby form a lubricating layer from such fine particle-containing resin (Patent Documents 3 and 4).
However, in the case of using a lubricating layer formed from a resin containing fine particles having a submicron particle diameter, light is scattered by such fine particles contained in the resin, and thereby the transparency or haze characteristics of the obtained transparent organic polymer substrate are impaired.
In this regard, some degree of transparency and low haze may be realized by decreasing the amount of the fine particles contained in the resin. However, in such a case, it is sometimes difficult to obtain sufficient lubricity.
Also, in the case of using a lubricating layer formed from a resin containing fine particles having a submicron particle diameter, when a writing durability test is performed, particles that form the protrusions on the surface of the transparent electroconductive layer of the electrode substrate sometimes scatter in the touch panel. The thus-scattered fine particles may prevent electrical connection between a movable electrode substrate and a fixed electrode substrate, and thus deteriorate the electrical characteristics of the touch panel. Furthermore, the scattered fine particle may damage the transparent electroconductive layers of the movable electrode substrate and the fixed electrode substrate, and thus deteriorate the electrical characteristics of the touch panel.
In order to solve these problems, for example, Patent Documents 5 and 6 have proposed to form, on a transparent substrate film used as a transparent organic polymer substrate, an anchor layer having an uneven surface, which is formed of a resin containing ultrafine particles having an average primary particle diameter of 1 to 30 nm, and provide a transparent electroconductive layer thereon to obtain a transparent electroconductive film.
By disposing an anchor layer having an uneven surface on a transparent substrate film, sticking due to adherence of films is prevented in the resistance film-system touch panel. However, in order to allow the anchor layer to have an uneven surface by using ultrafine particles having an average particle diameter of 1 to 30 nm, a relatively large amount of ultrafine particles are contained in the anchor layer. Therefore, it is understood that the anchor layer has a relatively large haze value.